Extended Forecast Discussion NWS Weather Prediction Center College Park MD 1241 AM EDT Wed Oct 07 2020 Valid 12Z Sat Oct 10 2020 - 12Z Wed Oct 14 2020 ...Heavy rainfall likely from Hurricane Delta over parts of the Mid-South and East this weekend... ...Major pattern change expected for the western U.S. with cooler temperatures and increasing precipitation into early next week... ...Overview and Guidance Evaluation/Preferences... The medium range period (Saturday through next Wednesday) should exhibit a modestly amplified but still progressive pattern with a trough over the East that slowly weakens, while a trough moves through the West and amplifies over the Plains/Midwest/Great Lakes. Hurricane Delta is forecast to fly across portions of the Lower Mississippi & Tennessee Valleys while weakening as a robust cold front moves across the Plains early next week. There was a bit of model spread, with the 12z ECMWF the most amplified and slowest with the trough mid-continent with a very amplified upstream ridge not seen on any other piece of guidance, including the ensemble means. The 12z Canadian, 12z UKMET, and at times the 18z GFS (though it was on the fast side of the guidance) were closer to the ensemble mean solutions. Because of the greater spread than seen 24 hour ago, used more ensemble mean in the preference early to mid next week to account for the uncertainty. Weighted the QPF in the direction of the 18z GFS which was closest to the 03z NHC track of Delta. ...Weather/Hazard Highlights... Hurricane Delta is forecast to move from the Mississippi Delta and then northward/northeastward while weakening, becoming entangled in a front as it does so. This will spread heavy rainfall across the Gulf states/Tennessee Valley and into the Appalachians and perhaps Mid-Atlantic regions over the weekend. Localized intense rainfall may cause flash flooding along/near its track especially in areas that have seen an abundance of rainfall the past few weeks (central LA/MS where 14-day rainfall is 2-4X normal despite a recent dry period). Across the West, a potent trough will favor a period of somewhat cooler than average temperatures along the West Coast and into the Great Basin by Sunday. Additionally, precipitation will increase through the end of the week and this weekend across the West with snow possible in the higher terrain of the Cascades and the Northern/Central Rockies. This very much needed precipitation should provide some relief from ongoing fire weather concerns. Due to the relatively zonal flow/progressive pattern, areas east of the Rockies are expected to see near average temperatures due to downslope flow offsetting the cold advection, even in the wake of a cold front early next week. Record highs could be threatened across portions of NM/TX this weekend before the cold front/upper trough advance into the region. Record highs -- near 90F -- are also possible across southern Florida Sunday into Monday within the warm sector ahead of the polar front. Mild temperatures for mid-October are also expected into the Great Lakes ahead of the central states system on Monday and Tuesday and across the Northeast next Wednesday. Roth/Fracasso WPC medium range 500mb heights, surface systems, weather grids, quantitative precipitation, winter weather outlook probabilities and heat indices are at: https://www.wpc.ncep.noaa.gov/medr/5dayfcst500_wbg.gif https://www.wpc.ncep.noaa.gov/medr/5dayfcst_wbg_conus.gif https://www.wpc.ncep.noaa.gov/5km_grids/5km_gridsbody.html https://www.wpc.ncep.noaa.gov/qpf/day4-7.shtml https://www.wpc.ncep.noaa.gov/wwd/pwpf_d47/pwpf_medr.php?day=4 https://www.wpc.ncep.noaa.gov/heat_index.shtml